How do we see objects?

The Eye and the Brain

Stare at the centre of the rotating spiral for about 20 seconds, then look at your teacher

The Spiral Illusion

Understanding Sight

The tip of the candle flame emits light in all directions

But we only see the light that enters our Eye-Brain

Understanding Sight

We don’t see light that does not enter our eyes

Understanding Sight

We don’t see light directed away from our eyes unless it is reflected into our Eye-Brain by something

Understanding Sight

On diagrams in this unit, we will tend to ignore all light that does not enter our Eye-Brains

Light Rays

The path light takes is called a ray

Diagrams that show how light moves from the object to the eye are called ray diagrams

Light Rays

Can you see the Eye-Brain’s feet?

Light Rays

Light travels in straight lines

Since no ray of light can go straight from the Eye-Brain’s feet into your eyes, you can’t see them

Light Rays

Ray Diagrams

Luminous objects emit light rays in all directions

Ray Diagrams

Non-Luminous objects scatter the light rays from luminous objects in all directions

Ray Diagrams

Ray Diagrams

To make things simpler, we only show the rays coming from the top of the object

We always only show the light rays that enter the observer’s eye

Opaque Medium

An opaque medium absorbs or scatters all the rays

A textbook is an opaque medium